Agatha Christie 
Ordeal by Innocence 

Evidence that clears the name of a boy sentenced for killing his adopted mother arrives too late to save his life so who did kill her? According to the courts, Jacko Argyle bludgeoned his mother to death with a poker. The sentence was life imprisonment But when Dr Arthur Calgary turns up a year later with the proof that confirms Jacko s innocence, he is too late Jacko died behind bars from a bout of pneumonia. Worse still, the doctor s revelations re-open old wounds in the family, increasing the likelihood that the real murderer will strike again